(a) Field of the Invention
The present invention relates to a perforating machine for making tear lines in a woven or non-woven fiber sheet material.
(B) Description of Prior Art
In perforating paper, perforation is used primarily to direct a tear in the required location in the paper, a material that would otherwise tear easily without perforation. However, in the case of non-woven sheet material, particularly tough fiber, spun-bonded material, where the raw material is particularly resilient, it has proven difficult to provide effective perforated tear lines or wide webs of over 30". Perforations in this type material heretofore known, all but cut the web because the fibers are remarkably strong and only a few of these fibers are required to span the tear line in order to hold the sheet sections together along the tear line. Further, the differential between a web that will tear very easily and one that breaks in the process of re-rolling the perforated material is so small that any variation in tension, speed, etc., makes rewinding of a good perforated roll of such material exceedingly difficult. Also, materials which are impregnated with chemicals tend to cause a build-up of chemical on the rolls in a roll-type perforating machine, particularly whenever two rolls nip the fabric. It is, therefore, not possible to obtain traction by this type of an arrangement.
In order to perforate a web using the classical paper perforator, i.e., hardened steel rule dye revolving against a hardened steel roller, the male and female rollers must be large enough and strong enough not to deflect in the middle. If any deflection takes place when one is, for instance, cutting 0.003"-0.005" thick material, a 0.002" deflection will either not cut the web or burr the blade. It will also set up impossible vibration and wear. The only method for overcoming this is either to put in supports for the rolls, or use a larger and larger diameter roll, as the web width increases. In the case of an 80" web, it is estimated that the male and female roll diameters would have to be between 15" and 25" diameter in solid steel in order not to deflect 0.001". Since these type machines often require stopping and starting every 10 to 50 revolutions, the momentum inherent in such steel rollers makes such a design impractical.
In a known perforator for making tear lines in toilet tissue, a hacksaw blade rotates against a hardened neoprene or urethane insert on a female roll. The main problem in trying to adapt this type of machine to perforate nonwoven fiber material having tough fibers is that since there is no traction or friction between the female roll and the web, the male blade will merely depress the web into the neoprene pad without weakening the web. Accordingly, this type of perforator cannot perforate such material.